Elephant is phylum Chordata.
Step-by-step explanation:
Phylum Chordata is the phylum under the kingdom Animalia which contains the animals having notochord at any point of its life. Notochord is a cartilaginous structure that is present at the back of the organism in its embryonic life which gives support to the growing embryo. In some organisms like shark etc, they persists for whole life, while in vertebrates, they are replaced by vertebral column. They also show organ system level of organization, are triploblastic, bilaterally symmetrical, coelomate, do have ventral heart, dorsal nerve cord etc.
In elephant, we see all the features mentioned above. So elephant is a chordate, member of phylum Chordata.